When elastic pulses, in particular high power elastic pulses, such as those used in extra corporeal lithotripsy, propagate in a coupling liquid, the negative peaks which their wave form inevitably comprises generate pressure variations within the liquid and, when the local pressure drops below the saturating vapor pressure, vapor filled cavities may be formed within the liquid. As soon as these vapor bubbles reach higher pressure regions, they are suddently condensed.
The applicant has discovered that this cavitation phenomenon tends to slow down the propagation of any positive peak preceded by a negative peak and, consequently, to considerably reduce the power transmitted to the cells to be treated or to be examined by means of an elastic pulse generator and to cause different disturbances of the desired effects in the application of the elastic pulses to echography examination or to treatment by ultra-acoustic power concentration at a focal point. In extra-corporeal lithotripsy, the cavitation has the particularly important disadvantage of cause a prickly sensation which may reach the pain threshold.